1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device.
2. Background Art
A semiconductor oxide film has an important role as a gate insulation film in various kinds of semiconductor devices. In recent years, along progress of miniaturization of semiconductor elements, a thermally-oxidized film becomes increasingly thinner as a gate insulation film. In recent years, as the miniaturization of semiconductor elements has advanced, thermally-oxidized films serving as gate insulation films have become increasingly thinner. However, when the film thickness of a thermally-oxidized film becomes two nanometers or less, a current that passes through the thermally-oxidized film increases. An increase in the tunnel current brings about a phenomenon that an impurity such as boron contained in a gate electrode is caused to pass through the thermally-oxidized film and diffuses. Therefore, when the gate insulation film has a thin thickness of two nanometers or smaller, it is difficult to improve the performance of the semiconductor elements.
In order to overcome such a difficulty, a high-k gate insulation film produced by mixing nitrogen or metal into such an oxide film can be used. When nitrogen atoms or metal atoms are introduced into an oxide film, the dielectric constant of the gate insulation film is increased. Therefore, even when the gate insulation film has a large physical film thickness, an equivalent oxide thickness (EOT) of the gate insulation film can be made smaller. In other words, when a gate insulation film having a high dielectric constant is used, the thickness of the gate insulation film can be increased as compared to an ordinary oxide film having the same capacitance. With this structure, a current that leaks through the gate insulation film is decreased, and diffusion of impurity can be suppressed (Japanese Patent Application Laid-open No. 2002-63117).
However, when a P-type polysilicon electrode containing boron is formed on the gate insulation film having a higher dielectric constant than the oxide film, a flat band voltage Vfb and a threshold voltage Vth shift in accordance with the amount of nitrogen contained in the gate insulation film. Furthermore, a current flowing through a channel area immediately below the gate insulation film is scattered, thereby decreasing a drive current capability of the semiconductor elements. Furthermore, a leak current that tunnels through the gate insulation film is increased.